Just for clarity, helical cut gears are **ALWAYS** stronger than straight cut gears. They have a larger surface area engagement and therefore can transmit more torque than an equally sized straight cut gear. In addition they run quieter.

The downside is that since they are helical cut, there is now a component of load in the axial direction. This means that the shafting, and gearbox have to be stronger in order to resolve those loads without breaking, and that weight adds up quickly.

This is why race cars have straight cut gearing. It has nothing to do with the strength of the gears, and is everything to do with reducing weight.